In the manufacturing of coated products, it is often desirable to attain a coating having a substantially uniform thickness. This is especially true for products for optical or electronic applications.
The production of high quality articles, such as electronic, tape, optical, photographic, photothermographic, thermographic, abrasives, adhesive, display, and pharmaceutical articles, involves the application of a thin film of a coating material onto a continuously moving substrate or web. Thin films can be applied using a variety of techniques, including dip coating, forward and reverse roll coating, wire wound rod coating, and die coating. Die coaters include knife coaters, slot coaters, slide coaters, fluid bearing coaters, slide curtain coaters, drop die curtain coaters, and extrusion coaters among others. Many types of die coaters are described in the literature such as by Edward Cohen and Edgar Gutoff, Modern Coating and Drying Technology, VCH Publishers, NY 1992, ISBN 3-527-28246-7 and Gutoff and Cohen, Coating and Drying Defects: Troubleshooting Operating Problems, Wiley Interscience, NY ISBN 0-471-59810-0.
A die coater generally refers to an apparatus that utilizes a first die block and a second die block to form a manifold cavity and a die slot. The coating fluid, under pressure, flows through the manifold cavity and out the coating slot to form a ribbon of coating material. The uniformity of the coating layer depends on a number of factors including the uniformity of pressure across the coating slot, the uniformity of flow of the coating material across the coating slot, the precision of the coating slot through which the coating material (or extrudate) passes. Coatings can be applied as a single layer or as two or more superimposed layers. Although it is usually convenient for the substrate to be in the form of a continuous web, the substrate may also be formed to a succession of discrete sheets.